As shown in FIG. 1, a conventional telephone receiver is illustrated. The receiver is formed by a body 10, a yoke 20, a coil 30, a vibrating diaphragm 40, a front cover 50, and a rear cover 60. The outer side of the yoke 20 is circularly installed with a magnet 70. A circular iron piece 80 is attracted at the upper end of the magnet 70. The bottom of vent hole of the yoke 20 is adhered with a sound adjusting cloth 90 made of non-weaving cloth. In the prior telephone receiver, the body 10 and the rear cover 60 forms with a tightly sealed space so as to be connected to the sound adjusting cloth 90 to form a damp of the vibrating diaphragm. Thus, the prior art receiver may conform to the characteristic of the frequency response of a telephone receiver. However, in the aforesaid prior art telephone receiver, a rear cover 60 is necessary for being formed with a closing space. If the sealing of the closing space is not preferred in assembling, then a preferred frequency response can not be obtained. Whereas the assembly of the rear cover 60 is not convenient and complicated. Moreover, the rear cover 60 will increase the width of the receiver. Where it is used in a mobile phone or a super thin telephone (such as CT2), a bottleneck is induced due to the volume of the receiver can not be further reduced. This is a big problem in the conventional telephone receiver.
A frequency response of a conventional telephone receiver is shown in FIG. 5, wherein the effective bandwidth is ranged between 400 Hz.about.1.5 KHz. Thus the bandwidth is too narrow to generate a clear sound.